JPS63302825A - Electronic hemomanometer - Google Patents

Abstract

PURPOSE:To form the sampling pulse synchronous to the peak of a pulse wave signal with high accuracy, by separately detecting the peak part of a pulse wave signal by a threshold value variable comparator and a differentiation circuit and applying AND operation thereto. CONSTITUTION:A signal containing both of pulse wave data and pressure data of blood pressure is obtained by a pressure sensor 1 and subsequently amplified by a differential amplifier 2 to output a signal (a). This signal (a) becomes a pulse wave signal (b) by removing the DC component thereof to be respectively inputted to a threshold value variable type comparator 9, a differentiation circuit 7 and a sample holding circuit 11. The pulse wave signal (b) inputted to the comparator 9 is compared with threshold voltage VTH1 becoming reference and the pulse corresponding to the peak part of said pulse wave signal (b) is outputted by the comparator 9. The pulse wave signal (b) inputted to the differentiation circuit 7 is differentiated and a signal (c) having the peak value of the signal (b) as a cross point is outputted from the differentiation circuit 7. The AND of the signal (c) and a pulse signal (d) is taken by an NAND circuit 10 performing AND operation to output a pulse having a fine pulse width.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a blood pressure monitor, and more particularly to a circuit configuration of an electronic blood pressure needle using an oscillometric method.

(b) Prior art An electronic blood pressure monitor using an oscillometric method has been proposed (Japanese Patent Application Laid-Open No. 61-247432).

According to this electronic sphygmomanometer, blood pressure is measured by amplifying a pulse wave signal from a pulse wave sensor and then A/D converting it, and arithmetic processing of this digital data by a central processing unit.

(c) Problems to be Solved by the Invention However, since such conventional electronic blood pressure monitors are configured to directly amplify the pulse wave signal, when the pulse wave signal level increases, the output of the amplifier may become saturated, or conversely, the pulse wave signal When the signal level of the pulse wave signal becomes smaller, it becomes difficult to capture the peak level of the pulse wave signal.

Further, the pulse wave signal includes hump-shaped noise due to the compliance of the turnip band, but according to the conventional example, this hump-shaped noise may be erroneously detected as the peak of the pulse wave signal.

The present invention has been created in view of such conventional problems, and an object of the present invention is to provide an electronic blood pressure monitor that accurately detects only the peak value of a pulse wave signal and makes it possible to accurately measure blood pressure.

(d) Means for Solving the Problems The electronic blood pressure monitor of the present invention includes a comparator that changes the reference threshold level in accordance with the magnitude of the input pulse wave signal level;
A circuit that generates a sampling pulse based on the output of the comparator; a sample/hold circuit that operates in synchronization with the sampling pulse to capture the peak portion of the pulse wave signal; The present invention is characterized by comprising a control circuit that calculates a peak value of the input pulse wave signal and changes the threshold value of the comparator based on the result.

(e) The magnitude of the active pulse wave signal level differs from pulse wave signal to pulse wave signal, but in terms of time, the change gradually increases, or vice versa.

The present invention utilizes the properties of this pulse wave signal, and uses a control circuit to calculate the peak value of the previous pulse wave signal, and changes the reference threshold voltage of the comparator based on this result. As a result, the peak portion of the next pulse wave signal can be reliably and appropriately taken into the comparator. Therefore, the sampling pulse created based on the output of this comparator accurately corresponds to the peak of the pulse wave signal. Therefore, this sampling pulse allows the sample/hold circuit to reliably and highly accurately capture the peak value of the pulse wave signal.

(F) Embodiments Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of an electronic blood pressure monitor according to an embodiment of the present invention, and FIG. 2 is a timing chart illustrating its operation.

In the figure, (1) is a pressure sensor consisting of a resistance bridge and a constant current source that supplies current to the resistance bridge, and pulse wave information and pressure information of blood pressure can be obtained via the cuff band. (2) is a differential amplifier, which amplifies the output of the pressure sensor (1) as it is.

(3) is a bandpass filter that roughly removes body movements and noise. (4) is an A/D converter, which converts pressure information into digital information. This digital information is taken into the central processing unit (5).

(6) is a low-pass filter, which extracts the pulse wave signal from the output a of the filter (3) and removes high frequency components that adversely affect the acquisition of the peak of the pulse wave signal (output b). (7) is a differentiation circuit that differentiates the pulse wave signal,
A signal C having the peak value of the pulse wave signal as a cross point is output. (8) is a differential amplifier, which cuts one side of the signal C. Further, (9>) is a comparator that compares the pulse wave signal output from the filter (6) with the output (threshold value) of the D/A converter (13).

(10) is a sand circuit that performs an AND operation of the output signal C of the differential amplifier (8) and the output signal d of the comparator (9), and is a sand circuit that performs an AND operation of the output signal C of the differential amplifier (8) and the output signal d of the comparator (9). A pulse (sampling pulse e) is output. In this way, the sampling pulse C is generated based on the signal d, which is output by appropriately capturing the peak portion of the pulse wave signal by appropriately changing the threshold value. (11) is a sample/hold circuit which takes in the peak value of the pulse wave signal by using the output pulse of the NAND circuit (10) as a sampling pulse.

(12) digitizes the peak value of the pulse wave signal taken in by the sample/hold circuit (11) and
5). (13) is a D/A converter that converts the peak value digital data outputted from the central processing unit (5) into an analog quantity, and its output is inputted as the threshold voltage of the above-mentioned comparator (9).

FIG. 2 is a timing chart showing voltage waveforms at various parts of the circuit of FIG. 1, and the operation of the circuit according to the embodiment of the present invention will be explained with reference to this diagram.

First, the pressure sensor (1) obtains a signal containing both blood pressure pulse wave information and pressure information, and then the differential amplifier (2)
) is amplified and output (signal a in Fig. 2
). Next, noise caused by body movement etc. can be removed by a band pass filter (3) (signal a). This signal a is A/D
It is converted into a digital quantity by a converter (4) and sequentially stored in a memory circuit (not shown) via a central processing unit (5). Further, high frequency noise is removed from this signal by a low-pass filter (6), and a direct current component is removed, resulting in a pulse wave signal.

The pulse wave signal is input to each of a variable threshold comparator (9), a differentiation circuit (7), and a sample/hold circuit (11). The pulse wave signal input to the comparator (9) can be compared with the reference threshold voltage v141, and the comparator (9) outputs a pulse corresponding to the peak portion of the pulse wave signal. Further, the pulse wave signal input to the differentiating circuit (7) is differentiated, and the differentiating circuit (7) outputs a signal C having the peak value of the pulse wave signal as a cross point.

Then, the signal C and the pulse signal d are ANDed by a NAND circuit (10) that performs an AND operation, and a pulse with a minute pulse width is output (signal e). , this pulse signal e becomes a sampling pulse of a sample/hold circuit (11) to selectively take in the pulse wave signal.

According to the embodiment of the present invention, the peak portion of the pulse wave signal is detected separately by the comparator (9) and the differentiating circuit (7), and by performing a logical product operation, the time indicating the peak is determined with higher precision. Since this is used as a timing pulse to operate the sample/hold circuit (11), it is possible to accurately obtain the peak value of the pulse wave signal.

The peak portion of the pulse wave signal captured by the sample/hold circuit (11) is converted into a digital quantity by the A/D conversion circuit (12), and stored in a memory circuit (not shown) via the central processing unit (5>). At the same time, the pulse wave signal inputted next time is Since the peak portion is compared with the newly set threshold voltage VT,2, the peak value of the pulse wave signal can be appropriately captured.

(g) As described in detail of the invention, according to the present invention, only the peak portion of the pulse wave signal can be reliably captured by the variable threshold comparator. It becomes possible to create highly precisely synchronized sampling pulses. Therefore, the sample/hold circuit can reliably capture only the peak of the pulse wave signal, making it possible to obtain accurate maximum, average, and minimum blood pressure values.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an electronic blood pressure monitor according to an embodiment of the present invention, and FIG. 2 is a timing chart illustrating the operation of the circuit shown in FIG. 1. (1)...Pressure sensor, (2), (8)...
Differential amplifier, (3), <6>...filter, (
4), (12)...A/D converter, (5)...
・Central processing unit (CPU), (7)... Differential circuit,
(9)...Comparator, (10)...NAND circuit, (11)...Sample/hold circuit,
(13)...D/A converter.

Claims (1)

[Claims] (1) A comparator that changes a reference threshold level in response to the magnitude of an input pulse wave signal level, a circuit that generates a sampling pulse based on the output of the comparator, and a circuit that operates in synchronization with the sampling pulse. a sample/hold circuit that captures the peak portion of the pulse wave signal, and control that calculates the peak value of the pulse wave signal captured by the sample/hold circuit and changes the threshold of the comparator based on the result. An electronic blood pressure monitor characterized by having a circuit.